The technique of 125I-labeled peptide mapping has been improved and used to study both te primary structural relationships and surface exposure of the outer membrane proteins I, II, and III of several strains of Neisseria gonorrhoeae. In addition, the technique of high-performance liquid chromatography has been used both t analyze structural relationships nd to preparatively isolate 125I-peptides of interest for further structural, topographical, and immunological characterization.